The goal of this research project is to elucidate the mechanisms responsible for controlling expression of the cytochrome o oxidase (cyoABCDE) and cytochrome d oxidase (cydAB) genes in the enteric bacterium, Escherichia coli. These two operons encode the two alternative enzyme complexes for oxygen reduction. They are expressed optimally under aerobic or micro-aerobic conditions and allow the cell to generate a chemiosmotic potential for subsequent ATP generation via the proton translocating ATPase. This potential is also used for proton driven solute uptake and for cell motility. The enzymes encoded by cyoABCDE and cydAB genes are representative of the cytochrome oxidases in many other microorganisms including the enteric bacteria, various facultative soil bacteria and for at least some of the obligate aerobic bacteria. We propose to study the regulation of the cytochrome o (cyoABCDE) and cytochrome d (cydAB) oxidase genes of E. coli as a model to understand how these aerobic cell functions are regulated in response change in environmental conditions. Little is yet known about the mechanisms responsible for this control. We will study the role of the fnr, arcA, and himA gene products in these processes to better understand the mechanisms by which they act. Control of cytochrome d oxidase (cydAB) gene expression will be examined by localized mutagenesis and screening for cis-acting regulatory mutations. DNA binding studies will be performed to locate regulatory sites for the Fnr and ArcA proteins. Similar studies will also be done with the cytochrome o oxidase (cyoABCDE) genes to determine how the Fnr and ArcA proteins affect their expression. The role of CAP in cyoABCDE expression will also be examined. To understand how the levels of the arcA and arcB gene products vary in the cell, their expression will be examined using lacZ fusion vector systems. Finally, the effect of oxygen concentration and growth rate on cyoABCDE and cydAB gene expression will be tested to better understand the physiology of oxygen use by E. coli cells.